As is known, a microchannel plate (MCP) includes an array of small diameter tubes or channels, each of which operates as an independent electron multiplier in the presence of an electric field applied to the MCP. As a signal (e.g., an electron, photon, ion) enters the input end of a given channel and passes through that channel, it impacts the channel walls thereby producing so-called secondary electrons that then also propagate through the channel and impact the channel wall to produce even more secondary electrons. This repetitive addition of electrons effectively amplifies the original input signal by several orders of magnitude, depending on factors such as strength of the electric field and channel geometry.
A collector electrode (generally referred to as an anode) is provided at the other end of the channel to collect the multitude of electrons (sometime referred to as an electron pulse or cloud). While some MCP designs have a single anode to collect total current produced by all channels, other MCP designs have a multi-anode configuration where each channel has a dedicated anode. Such a multi-anode MCP configuration is particularly useful when it is necessary to maintain spatial relationships of input signals (e.g., such as the case with imaging applications).
MCP devices can be used in a number of detectors for military, scientific and commercial applications. In general, a detector that employs MCP technology includes a converter (e.g., photocathode) to convert the incident photons into electrons, one or more MCPs that operate to amplify the initial electron or photon event into an electron cloud, and a readout circuit for receiving each electron cloud and converting it into a signal having qualities suitable for subsequent signal processing. MCPs are in general sensitive to photons by a much lower efficiency than a photocathode. In some cases, however, where the MCP is directly sensitive to the target event or particle, no converter is needed (e.g., such as in ion detection in mass-spectrometry applications, and UV and VUV radiation detection applications). In other cases, the converter may further include a scintillator that converts incident particles into photons that are subsequently converted to electrons by a photocathode or other suitable conversion mechanism.
A problem associated with conventional MCP-based detectors is that MCPs typically have large active areas (active areas of 18 and 25 mm in diameter are standard), which are useful in collecting signal, but require a correspondingly large sized readout integrated circuit (ROIC). In short, it is difficult and expensive to fabricate a ROIC that is compatible with such large sized MCP active areas.
One solution to this problem is to effectively reduce the size of the image produced by the MCP sensor by using an optical taper (which typically involves a conversion from electrons to light at the MCP output using a phosphor), thereby allowing a smaller ROIC to be used. However, this conversion from electrons to photons and then back to electrons for signal processing increases the cost, size, weight and power of the detector. It also reduces the system modulation transfer function (MTF), detection efficiency, and reliability. Another solution involves abutting a plurality of ROICs to form a larger readout device. Large arrays can also be made by field stitching. Certain applications, however, cannot tolerate the increased cost and/or loss of pixels at the interface between ROICs associated with such options.
There is a need, therefore, for techniques that can be used to interface an MCP device with readout circuitry.